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Covid-19 cases have been confirmed on one of the first
cruise ships to travel around the country in more than
two years.
Ovation of the Seas, carrying almost 5000
passengers and 1300 crew, sailed into Napier on Monday from
Tahiti, and arrived in Wellington this morning.
The
SMC asked experts to comment.
Professor
Michael Baker, Department of Public Health, University of
Otago, Wellington, comments:
“The role of
cruise ships in relation to Covid-19 in New Zealand has
changed fundamentally since the early days of the pandemic
in March 2020. At that stage New Zealand was managing its
external borders very tightly to limit, and then prevent
importation of Covid-19 entirely as part of its elimination
strategy.
“Now that we have more than 10,000 people
a day arriving on flights into New Zealand, with no
requirements for Covid-19 vaccination or testing, our
borders are largely open. In this context, cruise ships can
only make a relatively small contribution to Covid-19
importation. Their infectious disease control protocols may
now be stronger than for air travel, with passengers
sometimes required to be vaccinated and test Covid-negative
prior to embarking.
“The Ovation of the Seas cruise
ship, which arrived in Wellington today, is carrying about
4500 crew and passengers so it is not surprising that there
is transmission of Covid-19 on the ship. Infected cases are
required to isolate on board, which will reduce but not
prevent some of them potentially bringing infections with
them when they leave the ship. From a risk assessment
perspective, it would be useful if these ships were required
to report the number of infected passengers and crew
onboard. This should be part of their process of pratique
prior to them arriving in our ports and the information
should be made publicly available.
“Much of the
concern about managing Covid-19 on cruise ships will now be
about protecting the health of their passengers. Even prior
to Covid-19, cruise ships were notorious for outbreaks of
infectious disease. Much of this heightened risk is from
having thousands of people spending days at a time living in
a densely packed confined environment with many shared
facilities where gastroenteritis and respiratory infections
can spread easily. The generally older demographic of cruise
ship passengers makes them more vulnerable to infection and
becoming seriously ill.”
No conflict of
interest.
Dr Emily Harvey, Co-lead of the
Contagion Network modelling programme, COVID-19 Modelling
Aotearoa, comments:
“Now that border
restrictions and public health protections have been lifted
in most countries around the world, we should expect that a
proportion of international arrivals, be it by air or cruise
ship, will be infected with COVID-19 when they
disembark.
“We have consistently seen that
international air arrivals, even when we required
predeparture testing, had high levels of COVID infection —
similar to or higher than the estimated prevalence in their
country of origin. Some of this can be attributed to the
increased risk of infection during travel. As an example, in
mid-2022 when we had good reporting on border case numbers
from compulsory RAT testing during the BA5 wave, we had the
proportion reporting positive RATs get as high as 5-6% in
international arrivals. This was in line with the ~6%
prevalence peak seen in the UK during that period, which is
the only country that conducts a regular infection
prevalence survey.
“International arrivals by both
air and cruise ships add increased risk of introduction of
new variants, and can lead to an increase in infection risk
in the community if the prevalence is higher in the country
of origin than in Aotearoa.
“Although the number of
people arriving on planes is far greater than by those
arriving on cruise ships, there are a few key differences to
consider.
“If we know the background prevalence,
there is a
calculation that we can do to estimate the likelihood
that someone in a
randomly selected group has COVID-19.
“Using
this maths, we can estimate that on a plane with 300
passengers, with a background prevalence of 1%, the chance
that someone on your plane is infected is 78%. Now thinking
about cruise ships, which are larger, we would estimate that
on a cruise ship of 2000 people, with a background
prevalence of 1% the probability that at least one of them
is infected at the start of the trip approaches
100%.
“As context, with the current ‘lull’ in
levels of COVID-19 prevalence, prevalence sits around 3% in
the UK at the moment (which is the only country that
conducts a regular infection prevalence survey), or around
1% in NZ (if we assume case ascertainment rates of around
35%, but we really need an infection prevalence survey
here).
“Confirmed transmission on aircrafts has
mostly been to a small number of people sitting nearby.
However, as we have seen in past years, the longer duration
and shared facilities on cruise ships has meant that a small
number of infected passengers has often led to large
outbreaks. Whether this continues to occur will depend on
the infection control measures that are being implemented
onboard the ships. I would hope that the required reporting
under the Maritime Declaration of Health was being enforced
and monitored by Public Health Officials, and additional
measures taken if larger outbreaks were being
detected.
“Rapid antigen tests are good at detecting
when people are most infectious. Requiring a negative RAT
result to disembark would be a simple measure that would
help reduce the possibility of infectious passengers coming
ashore.
“Additionally, although the number of
international passengers arriving in Aotearoa on cruise
ships is dwarfed by the number arriving via air travel at a
national level, it is important to consider that for some
regional ports in smaller towns cruise ship arrivals will
add a substantial extra number of international
visitors.
“Finally, the age profile of cruise ship
passengers (75% being over 50, and half being over 65), adds
an additional risk to consider, because these age groups are
at much higher risk of needing hospital level care if
infected with COVID-19. An outbreak within a cruise ship has
the potential to add to the burden on our hospital system,
which would again be an even greater issue in smaller
regional port cities, with lower hospital
capacities.”
Conflict of interest statement:
“Dr Harvey’s employer receives funding from the DPMC for
her to provide modelling and analysis to government
officials on Aotearoa’s COVID response, and from the NZ
Health Research Council for a project on modelling and
equity for COVID-19 in
Aotearoa.”
© Scoop Media
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