Many Dutch people have already had at least 3 vaccinations against Covid-19, in all kinds of vaccination combinations. But what is the most effective set? Researchers from Hong Kong conducted a network meta-analysis looking at what was known about the efficacy of heterologous and homologous covid-19 vaccine combinations up to March 8, 2022 (BMJ. 2022;377:e069989). They found 53 studies with varying designs, participants and outcome measures, which examined 24 different combinations in terms of vaccines administered and number of doses.
People who received an mRNA vaccine 3 times appeared to be best protected against Covid-19 infection and Covid-19-related hospitalization (effectiveness compared with unvaccinated 96% (95% CI: 72-99) and 95% (95 % CI: 90-97)). An mRNA booster after 2 adenovirus vaccines also worked quite well against Covid-19 infections (88% effective; 95% CI: 59-97).
Subgroup analyzes indicated that 3 mRNA doses provide comparable protection to people with weakened immune systems. Also, homologous and heterologous triple vaccinations seemed effective against different variants – fewer vaccinations were ineffective against omikron in any case. In addition, 3 doses of vaccination were shown to provide comparable protection in all age groups.
The researchers conclude that the number of doses does more for immunity than the combination of different types of vaccines, but that mRNA vaccines are preferred for both primary and booster shots.