1. Can children be vaccinated against Covid-19?
Salim Abdool Karim (SAK): No, children below the age of 16 should not be vaccinated at this time because of a lack of safety and efficacy data in this age group.
This is expected to change soon: the Pfizer vaccine is awaiting regulatory approval for children of 12 to 15 years based on its recently completed clinical trial in the US that showed that this vaccine is safe and efficacious in this age group.
[Bhekisisa: The Pfizer trial showed 100% efficacy among children between the ages of 12 and 15. The company is currently testing its vaccine on kids between six months and 11 years old.]
Studies to generate similar data on the other vaccines and on younger children are underway.
Although safety and efficacy information from most adult trials is available only for those 18 years and older, some jabs, for instance, Pfizer, have this information for 16 years and older.
Also, children (compared to adults) are a lower priority for vaccination because they are at a substantially smaller risk of becoming ill when infected with SARS-CoV-2.
[Bhekisisa: In South Africa, the Pfizer jab received section 21 authorisation in March (section 21 means emergency-authorisation use), for use on people of 18 and older.]
We should have more safety and efficacy data for children in three to four months from now, so in about August, because Moderna and AstraZeneca [Bheksisa: the AstraZeneca trial was temporarily paused on 7 April because of safety concerns] have also started with studies. Other manufacturers are not far behind, and are either in advanced stages of planning such trials or about to start them.
Companies need sufficient data to be able to apply for vaccines to be used on children; until then, we can’t vaccinate children.
2. Is it safe to vaccinate pregnant women with Covid vaccines?
SAK: Overall, I would recommend that if a pregnant woman is in a high-risk situation, she should get vaccinated during pregnancy. An example of high-risk is a frontline healthcare worker. If, on the other hand, the pregnant woman is at lower risk, I would advise waiting until the end of pregnancy.
Until now, there has been little evidence from the Covid-19 vaccines to conclusively establish their safety in pregnant women. Based on the preliminary evidence that we have so far, there are a varying range of recommendations from the Centres for Disease Control (CDC) in the US, the World Health Organisation (WHO) and a range of other organisations.
They all provide slightly differing advice.
[Bhekisisa: The CDC says pregnant women are more likely to fall severely ill with Covid-19 than non-pregnant women because they have compromised immune systems. According to the WHO, Covid-19 has been associated with an increased risk of babies being born before their expected delivery date.
None of the Covid vaccine trials that tested the safety and efficacy of a particular jab chose to include pregnant women, so that is why our direct knowledge of the effect of Covid shots on pregnant women and their babies is limited. However, studies in animals receiving a Moderna, Pfizer-BioNTech, or Johnson & Johnson’s Janssen (J&J/Janssen) Covid-19 vaccine before or during pregnancy found no safety concerns.
A study published in March showed that Moderna and Pfizer’s jabs generated the same type of immunity in pregnant and breastfeeding women as in non-pregnant women. The CDC is also following about 30 000 vaccine recipients who were pregnant at the time of getting their jab(s). Almost 1 800 participants have provided detailed descriptions of their pregnancy outcomes and the symptoms they experienced after they got vaccinated. So far, pregnant people appear to have the same vaccine side effects as non-pregnant individuals. No miscarriages, stillbirths, or preterm births linked with the vaccines have been reported.
The WHO recommends that, because evidence on the effects of the Johnson & Johnson jab on pregnant people is limited, they should receive this vaccine only if “the benefit of vaccination to the pregnant woman outweighs the potential vaccine risks, such as if the woman is a health worker at high risk of exposure or has comorbidities that place them in a high-risk group for severe Covid-19”.
But the CDC points out that vaccines similar to J&J’s jab (shots that use the same type of harmless virus to deliver immune instructions to our cells), such as the Ebola vaccine, have not been associated with any “adverse pregnancy-related outcomes”.
The CDC says vaccines should be offered to eligible pregnant people and that, if you’re trying to become pregnant, “you do not need to avoid pregnancy after receiving a Covid-19 vaccine”.]
3. Can Covid vaccines prevent you from becoming infected with SARS-CoV-2 (the virus that causes Covid-19) or do they just protect you from falling ill?
SAK: There are two important points to consider in addressing this question. Firstly, when we mention a Covid-19 vaccine’s efficacy, we are only referring to its ability to prevent clinical illness with symptoms such as fever, cough, et cetera. Secondly, preventing clinical illness does not equate to preventing infection, because many cases of coronavirus infections are asymptomatic. In asymptomatic infection, the person does not even know that (s)he was infected at all.
We, however, have very little information on whether the vaccines can reduce asymptomatic infections.
[Bhekisisa: Studies suggest that about half of all Covid cases are asymptomatic.]
Only one vaccine clinical trial (of the AstraZeneca vaccine in the UK) attempted to assess the efficacy in preventing all infections, regardless of whether there were symptoms. This study, which tested participants for asymptomatic infection with PCR tests, showed lower protection against asymptomatic infections compared to symptomatic illness.
In the AstraZeneca study, researchers asked participants to do weekly nasal swabs at home that were then sent to labs for PCR Covid tests [Bhekisisa: PCR tests are the most commonly used Covid tests that detect the actual virus in a lab. The data showed that there was a 49.3% reduction in asymptomatic infections among the subset of vaccinated participants in the AstraZeneca trial.]
The challenge, however, is that you can miss infections with PCR tests if you only test people once a week and it also doesn’t tell you if the person had been infected previously.
[Bhekisisa: PCR tests are great at detecting the virus in patients with acute infection — in other words, those who have clear symptoms — but not so great at picking up the virus in those with mild symptoms and who are in the very early or very late stages of infection, when there is not enough virus present in someone’s system for the test to detect it.]
The way in which several of the other studies will be looking at asymptomatic infections is to measure SARS-CoV-2 antibodies on entry into the study. In other words, to establish whether this individual had been infected before the trial. They will then take another antibody test at the end of the study. So in those individuals who started the study with no SARS-CoV-2 antibodies, which means there’s no evidence of past infection, we can look at whether they acquired asymptomatic infection using antibody tests.
One of the challenges, however, is that the vaccines themselves generate antibodies. So the vaccines can cause a false positive antibody test. But there’s a way around that problem. We can measure antibodies that are not included in the vaccine — there are a whole range of SARS-CoV-2 antibodies that are not generated by the vaccine; the vaccines are all focusing on generating antibodies produced in response to the surface spike protein of the virus. So if we look at SARS-CoV-2 antibodies against parts of the virus that are not spike proteins, we can measure whether somebody became infected naturally.
[Bhekisisa: a preprint study from an antibody study led by the CDC and published in The Lancet in February found that the Pfizer and Moderna jabs reduce asymptomatic infections by 90% after two doses and 80% after one dose. The study followed essential workers through the worst months of the US’s pandemic.]
4. How often will we have to get vaccinated — so how long does the immunity we get from vaccines last?
SAK: Because the first Covid vaccine clinical trials were initiated less than a year ago, we don’t have empirical information about the longevity of the immune response that’s generated by vaccines.
[Bhekisisa: Pfizer and Moderna are two of the vaccines that have been around the longest because the development of the jab started very early on in the Covid pandemic.]
Both studies showed that the protection against symptomatic Covid-19 remains exceedingly high, at about 91% up to six months after the second dose.
The Pfizer vaccine trial included a modest number of South African participants, and as expected, the vaccine has been shown to protect against the 501Y.V2 variant. So that’s good news for South Africa, because the Pfizer vaccine is among those that we are considering rolling out.
[Bhekisisa: The Pfizer trial found the jab was 100% effective in preventing Covid-19 cases in South Africa among a group of 800 participants. Six out of the nine Covid-19 cases that occured, all in the group that received a dummy vaccine, were caused by the new 501Y.V2 variant. A small cross-sectional survey in Israel, however, showed that vaccinated people were more likely to become infected with the 501Y.V2 variant, compared to the likelihood of becoming infected with the original form of the virus, suggesting that the vaccine could be less effective against the 501Y.V2 variant. But it’s important to point out that cross-sectional surveys cannot establish cause and effect, rather, they are mostly used to gather preliminary data to support further research.]
We do not yet have evidence on vaccine efficacy that goes beyond six months.
[Bhekisisa: We first need to wait for vaccines to be around for long enough before we can measure whether immunity lasts for beyond six months. Preliminary data suggests Moderna’s vaccine offers similar protection so far, according to a letter published in The New England Journal of Medicine on 6 April. Researchers found that “antibody activity remained high” for six months after the second dose, but the study hasn’t yet been published.]
What I think will happen is that we’ll find that the antibody levels will remain high for a substantial period, meaning for a few years — after that we might find the antibodies waning. The chief executive of Pfizer has just announced that booster doses of its vaccines are going to be needed. This is most likely to be based on estimates of when antibody concentrations decline to a level where they may not be enough to protect against infection.
5. When will we have a vaccine that protects specifically against the 501Y.V2 variant?
SAK: Soon, I expect. Moderna has already created such a vaccine, and that vaccine is already in clinical trials. Pfizer, Johnson & Johnson and AstraZeneca are either in the process of developing such vaccines or in the process of testing them.
Variants occur across the world, because all viruses mutate, not just SARS-CoV-2. We’re not concerned about all of the different variants and mutations; we’re interested mostly in variants where there are mutations that occur to the part of the virus that binds onto the human cell — in SARS-CoV-2 that area is called the receptor binding domain.
When we see variants that have significant mutations to the receptor binding domain, we call them “variants of concern”.
So what are we concerned about? We want to know if the variant and its mutations enable the virus to spread faster, whether they cause more severe disease or if the variant can escape natural immunity. What we are most concerned about is: Do vaccines protect against new variants?
Here’s what we know about the 501Y.V2 variant. The AstraZeneca vaccine, which has shown to be about 70% effective in the UK and Brazil, was 22% protective in South Africa. The Novavax vaccine, which was about 90% effective in the UK, was only 49% effective in South Africa. So we have been seeing declines in clinical efficacy for some of the vaccines against the 501Y.V2 variant.
On the other hand, there are vaccines that seemed to work quite well against the variant. The Pfizer vaccine is a clear example of that, where the data that’s available, admittedly from a small study, shows that the Pfizer vaccine is 100% effective against the 501Y.V2 variant. The J&J vaccine was 72% effective in the US and 64% effective in South Africa, showing that the 501Y.V2 variant had less of an effect on this vaccine.
So we are seeing different vaccines responding in different ways and that they have different capabilities against variants like the 501Y.V2. It should be noted that, although all these trials set out to measure all clinical cases of Covid-19, some had no or few cases of severe disease, resulting in less clear effects of some of the vaccines on severe disease caused by 501Y.V2. Given that the existing vaccines have different levels of efficacy against the variant, several companies are developing “next generation vaccines”, specifically building around the mutations that occur in the 501Y.V2 variant.
As the virus evolves and more variants emerge, we will see the development of more new vaccine candidates. They can either be booster doses on existing vaccines or completely new vaccines to target these variants.
6. How difficult will it be to adjust vaccines for variants overtime?
SAK: Making new versions of Covid vaccines based on emerging variants is actually not that difficult. It’s easier for some of the technologies and slightly more difficult for others.
The Pfizer and Moderna vaccines, which are based on mRNA technology, can be adjusted quite quickly, because you have to change the genetic sequence, which can be done relatively fast.
However, for viral vector vaccines, such as the J&J, SputnikV or the AstraZeneca vaccines, this is technically a bit more complicated and takes a bit longer.