Don’t waste time making head to head comparison of vaccines, the best vaccine is the one you take

Apr 16, 2021 Letters

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DEAR EDITOR,

It seems commentary and some people’s attitude (in every part of the world) cannot move away from ‘I want the best COVID-19 vaccine’ which mainly translates to vaccines with high efficacy in clinical trials.
Hence, this is a reminder that the main goal of vaccination campaigns is to get a significant proportion of the population vaccinated to the point where person to person spread is unlikely. It’s prioritising the collective but with individual benefit in the end. The faster people realise this, the better the chances of beating this pandemic – sooner than later (globally). I say sooner because it’s not going to happen soon. We are stuck with the coronavirus and its variants for a while – that’s the reality. So, the best thing we can do to counteract this is to get vaccinated and still practice control measures (hand washing, social distancing, wearing a mask, etc.) until we’ve driven down transmission to a minimum. Eventually, in years to come, maybe it will be eradicated. This is going to take quite some time.
Get vaccinated because you are giving yourself a major boost to fight the virus by allowing yourself to build immunity (without being infected with the virus) and stock up on antibodies (our soldiers in our body’s defence system at war with the virus). At the same time keep up the control measures like wearing your mask because it will take time for you to develop immunity and make antibodies once vaccinated. In addition, although you may be boosted or don’t become ill and death is prevented with vaccination, you can still become infected and asymptomatic and therefore be a virus spreader, so others aren’t safe – again, caring for the collective is the best way to beat the pandemic. Further, if there are a significant number of people susceptible to infection, the virus still has the opportunity to try to evade our immune system by mutating into worse forms; forms which may render current vaccines ineffective. So, until a significant portion of the population is immunised, the control measures are very necessary. In the words of the WHO director, “No one is safe, until everyone is safe.”
Get vaccinated with the vaccine available unless there is evidence to show that the vaccine just does not work. To my knowledge, all approved vaccines are effective. Note however, that lining them up head to head to compare according to efficacy (in clinical trials) is a waste of time and shouldn’t factor into the decision to get vaccinated. This is why:

1. All vaccine efficacies are calculated the same way but clinical trials for the different vaccines were done in different places under different conditions. To align the vaccines and compare efficacies, the clinical trials would have to be done in the same place under the same conditions.

2. Efficacy is a measurement done usually in large scale Phase 3 clinical trials (10s of thousands of participants). Half of the participants get the vaccine while the other half is given a placebo. They are then monitored for COVID-19. In the Pfizer/BioNTech vaccine trial there were 170 cases of COVID-19 out of a total of 43,448 participants injected (F. Polack et al., NEJM, 2020, 383, 2603-15).The number of cases in each group (placebo vs. vaccine) was used to calculate the efficacy. If the number of cases in each group were equally split, then the vaccine would be considered 0% effective. If all cases were in the placebo group, then it would be 100% effective (no one given the vaccine got sick). What happened in the trial is that 162 people in the placebo group got COVID-19 while just 8 in the vaccine group got it. This corresponds to 95% efficacy – so an individual who got the vaccine was 95% less likely to get COVID-19. So, a trial conducted at a time with more overall infections will likely results in a lower efficacy.

3. Vaccines target specific strains/variants of a virus and if/when there are new forms the efficacies may vary and current vaccines may need to be modified to maintain efficacy (as done for the flu vaccine as the influenza virus is notorious for mutating to produce new strains/subtypes and vaccine effectiveness averages 40-60%).
We have seen this with the Coronavirus variants that have emerged where there is a decreased efficacy of current vaccines and in one case of it being ineffective against the variant (the Oxford-AstraZeneca vaccine against the dominant variant in South Africa).
Additionally, the trials (in which efficacies were measured) for the different vaccines were done at different times in the pandemic when a different proportion of variants were circulating. The Pfizer/BioNTech and Moderna trials were predominantly done in the US at a time in the pandemic where infection numbers were a lot less than when the Johnson and Johnson trials were conducted. In addition to the US, the Johnson and Johnson trial comprised a significant portion of participants in Brazil and South Africa where there were more contagious variants emerging (B.1.351 in SA and P.1 in Brazil) in addition to a high number of infections, so it’s not surprising that the efficacy measured for the J&J vaccine was less than that of the other two vaccines (where trials were conducted when it was mainly the original strain circulating).
Therefore, you can’t just line up the efficacies of the vaccines and say the best one is the one with the largest number. It’s not that simple as many other variables come into play. The vaccines currently being rolled out in Guyana – Oxford/AstraZeneca, Sinopharm and Sputinik V – were trialled in different parts of the world so a head-to-head comparison of efficacy is not meaningful.
The best vaccine is the one you take, as vaccination is the long-term tool to get out of the pandemic – when most are vaccinated and person-to-person virus transfer is suppressed. It takes a collective effort.

Sincerely,
Jacquelyn Jhingree, PhD

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